Microbial endophytes are present in all known plant species. The ability to enter and thrive in the plant tissues makes endophytes unique, showing multidimensional interactions within the host plant. ...Several vital activities of the host plant are known to be influenced by the presence of endophytes. They can promote plant growth, elicit defense response against pathogen attack, and can act as remediators of abiotic stresses. To date, most of the research has been done assuming that the interaction of endophytes with the host plant is similar to the plant growth-promoting (PGP) microbes present in the rhizosphere. However, a new appreciation of the difference of the rhizosphere environment from that of internal plant tissues is gaining attention. It would be interesting to explore the impact of endosymbionts on the host's gene expression, metabolism, and other physiological aspects essential in conferring resistance against biotic and abiotic stresses. A more intriguing and inexplicable issue with many endophytes that has to be critically evaluated is their ability to produce host metabolites, which can be harnessed on a large scale for potential use in diverse areas. In this review, we discuss the concept of endophytism, looking into the latest insights related to the multifarious interactions beneficial for the host plant and exploring the importance of these associations in agriculture and the environment and in other vital aspects such as human health.
Display omitted
•Melatonin is a multifunctional phytoprotectant to manage abiotic and biotic stresses.•Exogenous melatonin activates antioxidant system, regulates ion homeostasis and modulates plant ...defense in a stressed plant.•Melatonin mediated hormonal cross talk is integral in drought stress and viral disease mitigation.•Melatonin contributes to a sustainable horticultural production system.
Environmental stress and pathogen infection are the major limiting factors in worldwide horticulture production, resulting in huge yield loss. Melatonin (N-acetyl-5-methoxytryptamine) has gained a great interest in plant science research owing to its multifaceted role in plant systems. Melatonin mediated efficient reactive oxygen species scavenging and activation of antioxidant defence responses is the two major mechanisms to cope with most of the abiotic stresses and pathogen infections. Besides that, the activation of gene expression of stress-specific genes, antioxidant enzyme genes and pathogenesis-related genes make it a master regulator in plant defence responses under pathogen infection and environmental stresses. Additionally, hormonal cross-talk of melatonin with other phytohormones in regulating drought stress and virus infection gives an idea to explore the possibilities of such a mechanism in other stresses in diverse horticultural crops. The complementary effect of melatonin with fungicides is giving new hope in reducing the burden of exhaustive use of toxic chemicals in vegetables and fruit crops. Melatonin can play an essential role in combating sequential and simultaneous combined stresses in crop plants which are an emerging challenge these days. Our review highlighted the functions of melatonin in ameliorating major abiotic (heat, cold, drought, and salt) and biotic (fungi, virus, bacteria, and insects) stresses of horticultural crops and elucidated the resulting physiological and molecular mechanism. The versatile role of this biological molecule in anti-stress regulation showing successful cases of growth promotion and enhanced resistance makes it suitable for environment-friendly horticultural crop production and to ensure food safety.
Plants are constantly confronted to both abiotic and biotic stresses that seriously reduce their productivity. Plant responses to these stresses are complex and involve numerous physiological, ...molecular, and cellular adaptations. Recent evidence shows that a combination of abiotic and biotic stress can have a positive effect on plant performance by reducing the susceptibility to biotic stress. Such an interaction between both types of stress points to a crosstalk between their respective signaling pathways. This crosstalk may be synergistic and/or antagonistic and include among others the involvement of phytohormones, transcription factors, kinase cascades, and reactive oxygen species (ROS). In certain cases, such crosstalk can lead to a cross-tolerance and enhancement of a plant's resistance against pathogens. This review aims at giving an insight into cross-tolerance between abiotic and biotic stress, focusing on the molecular level and regulatory pathways.
Polyamines (PAs) are ubiquitous biogenic amines that have been implicated in diverse cellular functions in widely distributed organisms. In plants, mutant and transgenic plants with altered activity ...pointed to their involvement with different abiotic and biotic stresses. Furthermore, microarray, transcriptomic and proteomic approaches have elucidated key functions of different PAs in signaling networks in plants subjected to abiotic and biotic stresses, however the exact molecular mechanism remains enigmatic. Here, we argue that PAs should not be taken only as a protective molecule but rather like a double-faced molecule that likely serves as a major area for further research efforts. This review summarizes recent advances in plant polyamine research ranging from transgenic and mutant characterization to potential mechanisms of action during environmental stresses and diseases.
Plants are subjected to diverse biotic and abiotic stresses in life. These can induce changes in transcriptomics and metabolomics, resulting in changes to root and leaf exudates and, in turn, ...altering the plant-associated microbial community. Emerging evidence demonstrates that changes, especially the increased abundance of commensal microbes following stresses, can be beneficial for plant survival and act as a legacy, enhancing offspring fitness. However, outstanding questions remain regarding the microbial role in plant defense, many of which may now be answered utilizing a novel synthetic community approach. In this article, building on our current understanding on stress-induced changes in plant microbiomes, we propose a ‘DefenseBiome’ concept that informs the design and construction of beneficial microbial synthetic communities for improving fundamental understanding of plant–microbial interactions and the development of plant probiotics.
The recent advances in using synthetic communities together with metagenomics and metabolomics has begun to unravel mechanistic understanding of how stressed plants modulate their microbiomes.Stresses change plant transcriptomics and metabolomics below and above ground. Molecules such as flavonoids, coumarins, and other organic compounds have been recognized as plant signals that shape host microbiomes.A crucial regulating role of the interactions between the microbiome and plant immune system in stress tolerance is emerging. Experimental validation of such interactions and determination of how they influence plant fitness should now be prioritized.The plant-associated microbes that increase in abundance by plant stresses, coined the ‘DefenseBiome’, could benefit plant health and be used for designing functionally reliable synthetic communities to improve plant fitness.
Compelling evidence indicates that free polyamines (PAs) (mainly putrescine, spermidine, spermine, and its isomer thermospermine), some PA conjugates to hydroxycinnamic acids, and the products of PA ...oxidation (hydrogen peroxide and γ-aminobutyric acid) are required for different processes in plant development and participate in abiotic and biotic stress responses. A tight regulation of PA homeostasis is required, since depletion or over-accumulation of PAs can be detrimental for cell viability in many organisms. In plants, homeostasis is achieved by modulation of PA biosynthesis, conjugation, catabolism, and transport. However, recent data indicate that such mechanisms are not mere modulators of PA pools but actively participate in PA functions. Examples are found in the spermidine-dependent eiF5A hypusination required for cell division, PA hydroxycinnamic acid conjugates required for pollen development, and the involvement of thermospermine in cell specification. Recent advances also point to implications of PA transport in stress tolerance, PA-dependent transcriptional and translational modulation of genes and transcripts, and posttranslational modifications of proteins. Overall, the molecular mechanisms identified suggest that PAs are intricately coordinated and/or mediate different stress and developmental pathways during the lifespan of plants.
Plants are constantly exposed to various stresses, which can degrade their health. The stresses can be alleviated by the application of methyl jasmonate (MeJA), which is a hormone involved in plant ...signalling. MeJA induces synthesis of defensive compounds and initiates the expression of pathogenesis-related genes involved in systemic acquired resistance and local resistance. Thus, MeJA may be used against pathogens, salt stress, drought stress, low temperature, heavy metal stress and toxicities of other elements. The application of MeJA improves growth, induces the accumulation of active compounds, and affects endogenous hormones levels, and other physiological and biochemical characteristics in stressed plants. Furthermore, MeJA antagonises the adverse effects of osmotic stress by regulating inorganic penetrating ions or organic penetrants to suppress the absorption of toxic ions. MeJA also mitigates oxidative stress by activating antioxidant systems to scavenge reactive oxygen species (ROS) in stressed plants. For these reasons, we reviewed the use of exogenous MeJA in alleviating biotic (pathogens and insects) and abiotic stresses in plants.
Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, ...limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.
Our environment constantly undergoes changes either natural or manmade affecting growth and development of all the organisms including plants. Plants are sessile in nature and therefore to counter ...environmental changes such as light, temperature, nutrient and water availability, pathogen, and many others; plants have evolved intricate signaling mechanisms, composed of multiple components including several plant hormones. Research conducted in the last decade has placed Strigolactones (SLs) in the growing list of plant hormones involved in coping with environmental changes. SLs are carotenoid derivatives functioning as both endogenous and exogenous signaling molecules in response to various environmental cues. Initially, SLs were discovered as compounds that are harmful to plants due to their role as stimulants in seed germination of parasitic plants, a more beneficial role in plant growth and development was uncovered much later. SLs are required for maintaining plant architecture by regulating shoot and root growth in response to various external stimuli including arbuscular mycorrhizal fungi, light, nutrients, and temperature. Moreover, a role for SLs has also been recognized during various abiotic and biotic stress conditions making them suitable target for generating genetically engineered crop plants with improved yield. This review discusses the biosynthesis of SLs and their regulatory and physiological roles in various stress conditions. Understanding of detailed signaling mechanisms of SLs will be an important factor for designing genetically modified crops for overcoming the problem of crop loss under stressful conditions.
Summary
Human activity is causing a global change in plant environment that includes a significant increase in the number and intensity of different stress factors. These include combinations of ...multiple abiotic and biotic stressors that simultaneously or sequentially impact plants and microbiomes, causing a significant decrease in plant growth, yield and overall health. It was recently found that with the increasing number and complexity of stressors simultaneously impacting a plant, plant growth and survival decline dramatically, even if the level of each individual stress, involved in such ‘multifactorial stress combination’, is low enough not to have a significant effect. Here we highlight this new concept of multifactorial stress combination and discuss its importance for our efforts to develop climate change‐resilient crops.
PDF
